The invention relates to a method for operating an electrically controllable brake system for a motor vehicle with a master cylinder for generating a first brake pressure, with an electrically driven pump for generating a second brake pressure, and with at least one electrically driven valve arrangement for setting a pressure difference between the second brake pressure and the first brake pressure, and also to a method for operating an electrically controllable brake system for a motor vehicle with wheel cylinders in which a first brake pressure is generated, with an electrically driven pump for generating a second brake pressure, and with at least one electrically driven valve arrangement for setting a pressure difference between the second brake pressure and the first brake pressure. The invention also relates to an electrically controllable brake system that is operated in accordance with such methods.
From DE 102 47 651 A1 an electrically controllable brake system is known in which both the shut-off valves of each brake circuit, which are arranged between the master cylinder and the output of the pump, and also inlet valves assigned to the wheel brakes, which are arranged between the output of the pump and the respective wheel cylinder, take the form of electrically driven valve arrangements which have been designed for setting a pressure difference. A valve arrangement of such a type is known from DE 44 39 890 A10, and corresponding U.S. Pat. No. 6,120,003, both of which are incorporated by reference herein in entirety. Furthermore, from DE 10 2005 026 740 A1, and corresponding U.S. Pat. No. 8,271,172 B2, both of which are incorporated by reference herein in entirety, a method for driving a valve arrangement of such a type is known, according to which a setting of the pressure difference that is as accurate as possible is effected, so that brake pressures that are as accurate as possible are also generated, in order to obtain, particularly in automatic brake systems, a comfortable sequence of operations, for example without jerky movements and/or pulling of the vehicle.
The setting of a set-point value for the pressure difference and, besides that, the generating or setting of the desired brake pressures are ordinarily effected in a manner depending on the electric drive of the valve arrangement. For this purpose, in the electronic control unit of the brake system, for example, a characteristic map is saved, according to which the pressure difference can be controlled or regulated as a function of the electric current supplied to the valve arrangement.
In this connection there is the problem that the functional relationship between pressure difference and electric drive may be subject to considerable variabilities which result from the manufacturing tolerances of the hydraulic, mechanical and electrical/electronic system components involved. Added to these are tolerances that result from the ageing process and from wear of the system components in operation.